It is known to use support apparatus in the form of helical rods (“helicals”) for supporting and reinforcing electrical power transmission conductors. Helicals are used to form a number of different devices to carry out different supporting applications for conductors.
For example, helical dead-ends are used to support a conductor where there is an unbalanced mechanical load. Helicals are also used to splice together ends of conductors. Helical ties and side ties are used to attach a conductor to an insulator, and often consist of a single rod or a pair of helical rods. Spacers are used to separate conductors of the same voltage and may also consist of one helical rod or a subset or a set of helical rods. Armour rods are used to reinforce a conductor where it is connected (e.g. suspended) relative to a power or tower to avoid a stress riser being created at the area where the conductor is suspended. Other products for support, reinforcement, and protection of conductors are also produced using helicals.
There are a number of parameters associated with the quality of performance of a helical. These include coefficient of friction between the rod and conductor, angle of crossover (e.g. where helicals are used in dead-end applications); the springiness or hardness of the raw material from which the rods are made; whether the rods are glued together into subsets or sets, or applied individually; the pitch angle of the helical turns; the packing density; the length of each pitch; rod diameter; number of pitches, and compression ratio (the ratio of the internal diameter of the rod before application, to the external diameter of the conductor to which the rod is to be fitted). It is common practice for the purpose of ease of manufacture and simplicity of design to keep these parameters constant within each fitting.
Some helical devices have been made with variation in some parameters. For example, U.S. Pat. No. 2,172,810 discloses an armour rod with a narrower pitch at the ends of the rod than at the centre, which is said to promote greater flexibility at the ends. U.S. Pat. No. 3,899,629 discloses a helical fitting where the ends of the helical fitting have a longer pitch than the rest of the helical fitting, in order to allow the helical to be more easily installed on the conductor. The present Applicants believe that by manipulating the performance parameters associated with a helical rod, better, more efficient, support apparatus can be provided.